Breast cancer and soy
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By Ibby Caputo

Soy Safety

For breast cancer survivors, soy is back on the menu

By Ibby Caputo

After being diagnosed with stage II, estrogen receptor–positive breast cancer in August 2008, Jennifer Bolstad, like many cancer patients, wanted to keep as healthy a diet as possible. But the 33-year-old New York City–based landscape architect says she was perplexed by the mixed messages she had read about soy.

Soybean plantSome articles said soy could reduce breast cancer risk, while others warned that eating anything with soy might increase her risk of recurrence.

“Soy is good. Soy is bad,” Bolstad says of her findings. “I became completely confused.”

Bolstad’s confusion about soy is not surprising. Soy contains isoflavones, which act like a weak form of the body’s own estrogen. Scientists point to these isoflavones as the likely reason why some studies have found that soy may help lower cholesterol and blood pressure, prevent osteoporosis, reduce menopausal symptoms, ward off heart disease and reduce the risk of several types of cancer, including breast cancer. But when other findings from animal and laboratory studies suggested that these “good” isoflavones could promote the growth of breast cancer cells and decrease the effectiveness of the breast cancer drug tamoxifen, health care professionals began cautioning women who had estrogen-sensitive breast cancer to avoid soy.

It was a cumbersome challenge: Many survivors became worried about anything they ate because soy is found in everything from cereal to margarine.

So it was big news in the breast cancer community when a study published in the Dec. 9, 2009, Journal of the American Medical Association (JAMA) found that it is safe and potentially beneficial for women with breast cancer, including those who are taking tamoxifen, to eat soy foods. The women who ate the most soy food had a 29 percent lower risk of death and a 32 percent lower risk of having a cancer recurrence than did those who ate less than 5.3 grams of soy protein per day. The benefit to women increased with the more soy they ate, up to 11 grams of soy protein a day. Beyond 11 grams, the additional benefits leveled off. (Eleven grams of soy protein is the equivalent of half a cup of edamame, one and a quarter cups of soy milk, or four ounces of tofu.)

The population-based study, which included about 5,000 breast cancer survivors in Shanghai, China, is the largest soy study of its kind to date. “This is a very exciting observation for us,” says the study’s lead researcher, Xiao-Ou Shu, a cancer epidemiologist at Vanderbilt-Ingram Cancer Center in Nashville, Tenn. “We can say quite confidently that soy food is safe and potentially beneficial.”

But because not all soy is considered equal, women need to pay attention to what type of soy they are eating, and should avoid processed foods, like soy bars and soy supplements. “Doses are often different and the chemical structure may also differ in supplements,” explains Marian L. Neuhouser, a cancer epidemiology researcher at the Fred Hutchinson Cancer Research Center in Seattle, who wrote an accompanying editorial for the JAMA study.

Knowing the difference between whole and processed soy is important, says Neuhouser, because this study was done in China, where women are more likely to eat whole soy foods such as edamame, miso, tempeh, tofu and unsweetened soy milk than are women in the U.S.

Undoubtedly, much more remains to be learned about soy’s benefits and risks. That’s why Hillary Wright, a nutritionist at the Dana-Farber Cancer Institute in Boston, advises her breast cancer patients that if they are going to eat soy, to do so in moderation. “It’s the same old boring nutritionist’s message,” Wright says.

Perhaps. But it’s the best message Bolstad has heard. “Until there is hard and fast evidence that soy is to breast cancer what smoking is to lung cancer, I am going to eat it,” says Bolstad. “In moderation.”


(illustration: Corinne Lapin-Cohen)